1. Field of the Invention
This invention relates to a gate and shutter assembly for use in a luminaire, in other words a lamp unit, particularly, but not exclusively, for application in theatre, studio or other entertainment lighting, to provide a shaped spot of light.
2. Description of the Prior Art
In, for example, theatre lighting it is often desired to produce a square or rectangular patch of light so as to give the impression of light through a window, for instance. For this purpose, an aperture (gate) and shutter assembly is provided within the luminaire housing. The gate comprises a plate mounted transverse to the beam from the luminaire having a central aperture. A plurality of shutters (usually at least four) are provided each comprising a blade within the plane of the gate and a handle projecting out from the luminaire housing through a slot. By manipulating the handle for each blade, the operator can swivel the blade angularly through a range defined by the angular extent of the slot in the housing. He can also push the shutter in and out to reduce the amount of light passing through the gate. Commonly, two shutter blades are provided on either side of the gate, through slots disposed on opposite sides of the luminaire housing. The pair of shutters on one side of the gate is oriented at 90.degree. relative to the pair on the other side.
The extent of motion of each shutter blade is therefore dictated by the angular extent, round the luminaire housing, of the slot through which the handle of that shutter blade passes. Each slot must, of course, extend from the central cavity of the luminaire right through to the outside of the housing where it can be manipulated by a human operator. However, a luminaire is a heavy item of equipment, and one that is often moved from one place to another. It is therefore necessary for the luminaire housing to be relatively strongly built. The portion of the luminaire housing lying behind the gate and shutter assembly comprises the light source, associated electrical components and the ellipsoidal reflector directing light forwardly from the light source. The portion of the luminaire housing forward of the gate and shutter assembly contains imaging lenses, which produce a beam focussed from the plane of the gate, so that the shape formed by the shutters is the shape in cross-section of the beam projected on the stage.
There are thus heavy components at either side of the gate and the shutter assembly, and linking the two are the material within the lands between the slots. In order to provide sufficient structural strength to the luminaire housing, it has hitherto been necessary to provide relatively thick lands between the slots, and this has dictated the maximum angular extent of the slots.
Unfortunately, this has placed a constraint on the freedom of the user to align the shutter blades, and in particular the constraint that it has not been possible to manipulate a given blade through an angle approaching .+-.360.degree./2n, where n is the total number of shutter blades. Thus, in a four shutter arrangement it has not been possible to manipulate adjacent shutters (normally inclined at 90.degree. neutrally) to a blade inclination of 180.degree. (i.e parallel blades). This constraint limits the freedom of the lighting designer.
One solution previously adopted is to employ "off-set shutters"--that is, shutters in which the handle is not mounted in the centre of the shutter blade but is off-set to one side or at an angle to the blade. Such shutters are removable through the slots in the luminaire housing. In use, the operator can achieve a wider range of shutter angles by taking the shutter out, turning it over and re-inserting the other way round. However, there are several problems with this solution. Firstly, it is harder to use for an operator since a given handle position corresponds to two different shutter inclinations, depending on which way round the shutter is. Secondly, the shutter blades are, in use, subjected to intense heat so that they become red hot and warp. It is therefore difficult to remove and re-insert the shutters whilst the luminaire is in use or after the blades have become permanently distorted.